A bio-based epoxy monomer containing a Schiff base structure, a preparation method thereof, and applications thereof, and a bio-based epoxy resin containing a Schiff base structure, a preparation method thereof, and applications thereof

Abstract

The present invention provides a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application thereof, a bio-based epoxy resin containing a Schiff base structure, and a preparation method and application thereof, and relates to the technical field of epoxy resins. The bio-based epoxy monomer containing a Schiff base structure provided by the present invention contains a Schiff base structure. Based on the high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardancy and mechanical properties of the bio-based epoxy resin containing a Schiff base structure prepared using the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a small molecular weight, a high epoxy value, few side chain substituent groups, a simple structure, high symmetry, and a simple curing process with a curing agent. The obtained bio-based epoxy resin containing a Schiff base structure has a high glass transition temperature, excellent mechanical properties and thermal stability, and the dynamic cross-linking network exhibits good dynamic properties, and has huge application potential in the fields of flame retardancy, self-repair and biodegradable recycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of epoxy resins, and relates to a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application thereof, and a bio-based epoxy resin containing a Schiff base structure, a preparation method and application thereof. Background Art

[0002] Epoxy resin is a polymer material containing two or more epoxy groups in its molecular structure. Compared to other thermosetting plastics, epoxy resin has superior chemical and mechanical stability. It can be made into a variety of materials, including encapsulation materials, coatings, injection molding materials, adhesives, and more. It is widely used in daily life and various sectors of the national economy. Among the various types of epoxy resins, bisphenol A epoxy resin (DGEBA) is widely produced due to its simple synthesis process, accounting for over 85% of the total epoxy resin output.

[0003] Bisphenol A (BPA), the primary raw material for the most widely used DGEBA, is primarily derived from petroleum. With the increasing severity of petroleum depletion in recent years, humanity has been compelled to redevelop green, environmentally friendly, and sustainable biomass-based materials to replace non-renewable fossil resources and alleviate petroleum shortages. Furthermore, BPA, as an endocrine disruptor, can cause endocrine disorders and pose a serious threat to human health. Therefore, there is an urgent need to develop new bio-based epoxy resins from renewable resources to replace commercial petroleum-based epoxy resins.

[0004] In recent years, a large number of bio-based epoxy resins have been synthesized from various biomass resources. The abundance of monophenols in nature facilitates the synthesis of bio-based epoxy monomers. Schiff-base syringaldehyde-containing epoxy monomers have been reported. These monomers are prepared by reacting biomass syringaldehyde with an amino compound. The Schiff-base syringaldehyde-containing bisphenol monomer is then reacted with epichlorohydrin in the presence of a phase transfer catalyst, followed by a ring-opening reaction with sodium hydroxide solution to obtain the Schiff-base syringaldehyde-containing epoxy monomer. However, the epoxy resins prepared from these Schiff-base syringaldehyde-containing epoxy monomers suffer from insufficient thermal stability. Summary of the Invention

[0005] In view of this, the present invention aims to provide a bio-based epoxy monomer containing a Schiff base structure, a preparation method and application thereof, and a bio-based epoxy resin containing a Schiff base structure, and a preparation method and application thereof. The bio-based epoxy resin containing a Schiff base structure prepared using the bio-based epoxy monomer containing a Schiff base structure provided by the present invention as a raw material has excellent thermal stability.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

[0008]

[0009] The present invention also provides a method for preparing the bio-based epoxy monomer containing a Schiff base structure described in the above technical solution, comprising the following steps:

[0010] The bio-based bisphenol monomer, epichlorohydrin and a phase transfer catalyst are mixed to carry out a ring-opening reaction, and then an alkali metal hydroxide is added to carry out a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure;

[0011] The structural formula of the bio-based bisphenol monomer is as follows:

[0012] Preferably, the molar ratio of the bio-based bisphenol monomer to epichlorohydrin is 1:2.5-10;

[0013] The phase transfer catalyst includes one or more of organic ammonium halides, organic ammonium bisulfate, pyridine and organic amines;

[0014] The molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is 1:0.0125-0.2;

[0015] The ring-opening reaction temperature is 40 to 100° C., and the time is preferably 1 to 6 hours;

[0016] The molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is 1:0.5-2;

[0017] The alkali metal hydroxide is used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is 30-50%;

[0018] The temperature of the ring-closure reaction is less than 0° C., and the time is preferably 2 to 8 hours.

[0019] The present invention also provides the use of the bio-based epoxy monomer containing a Schiff base structure described in the above technical solution in the preparation of epoxy resin.

[0020] The present invention also provides a bio-based epoxy resin containing a Schiff base structure, and the raw materials for preparing the resin include the bio-based epoxy monomer and curing agent described in the above technical solution.

[0021] Preferably, the curing agent includes one or more of an organic amine curing agent, a carboxylic acid curing agent and an acid anhydride curing agent;

[0022] The mass of the curing agent accounts for 10 to 40% of the mass of the bio-based epoxy monomer.

[0023] Preferably, the preparation raw materials further include a promoter, and the promoter includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate and 2-methyl-4-ethylimidazole;

[0024] The mass of the accelerator accounts for 0.01 to 10% of the mass of the bio-based epoxy monomer.

[0025] The present invention also provides a method for preparing the bio-based epoxy resin containing a Schiff base structure described in the above technical solution, comprising the following steps: mixing a bio-based epoxy monomer and a curing agent, and curing to obtain the bio-based epoxy resin containing a Schiff base structure.

[0026] Preferably, the curing includes sequentially performing a first curing and a second curing; the temperature of the first curing is 40 to 120° C., and the time is 1 to 10 hours; the temperature of the second curing is 80 to 200° C., and the time is 1 to 10 hours; the temperature of the second curing is higher than the temperature of the first curing;

[0027] When the raw materials further include an accelerator, the mixing is to mix the bio-based epoxy monomer, the curing agent and the accelerator.

[0028] The present invention also provides the use of the bio-based epoxy resin containing a Schiff base structure described in the above technical solution or the bio-based epoxy resin containing a Schiff base structure prepared by the preparation method described in the above technical solution in flame retardant materials, self-repairing materials or degradable and recyclable materials.

[0029] The bio-based epoxy monomer containing a Schiff base structure provided by the present invention contains a Schiff base structure. Based on the high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardancy and mechanical properties of the bio-based epoxy resin containing a Schiff base structure prepared using the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a small molecular weight, a high epoxy value, few side chain substituent groups, a simple structure, high symmetry, and a simple curing process with a curing agent. The obtained bio-based epoxy resin containing a Schiff base structure has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties, and has great application potential in the fields of flame retardancy, self-repairing and biodegradable recycling.

[0030] The Schiff base structure in the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has dynamic chemical properties, and is cured by a carboxylic acid curing agent, an acid anhydride curing agent and an amine curing agent to form a cross-linked network structure containing dynamic imine bonds and dynamic ester bonds, which synergistically improves the dynamic performance of the epoxy resin cross-linked network. The strategy of applying dynamic chemistry to epoxy resins in the present invention can expand the multifunctionality of epoxy resins while designing high-performance epoxy resins on the molecular structure, thereby solving the problem that thermosetting epoxy resins are "insoluble and infusible" and difficult to recycle after cross-linking and curing. The present invention introduces reversible dynamic covalent bonds into the network of the bio-based epoxy resin containing a Schiff base structure, and then induces the network structure of the thermosetting resin to crack or rearrange through changes in the external environment, so that it has certain degradability and recyclability, which is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0031] As shown in the test results of the examples, the Schiff base structure contained in the bio-based epoxy resin containing a Schiff base structure prepared by the present invention has a carbon residue rate of ≥20% at 800°C (N2 atmosphere), a thermal weight loss temperature of 5% ≥260°C, and a glass transition temperature of up to 152°C, which is almost the same as that of commercial bisphenol A epoxy resin. It can replace traditional bisphenol A epoxy resin in some application scenarios.

[0032] The method for preparing a bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production.

[0033] The preparation method of the bio-based epoxy resin containing a Schiff base structure provided by the present invention has simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the novel bio-based epoxy resin containing a Schiff base structure prepared in Example;

[0035] Figure 2 This is a dynamic mechanical thermodynamic curve (DMA) diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 4;

[0036] Figure 3 This is a thermogravimetric analysis (TGA) curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 4;

[0037] Figure 4 This is a dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 5;

[0038] Figure 5 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 5;

[0039] Figure 6 This is a dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 6;

[0040] Figure 7 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 6;

[0041] Figure 8 This is a dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 7;

[0042] Figure 9 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 7;

[0043] Figure 10 This is a dynamic thermomechanical curve diagram of the bio-based epoxy resin containing a Schiff base structure prepared in Example 8;

[0044] Figure 11 This is a thermogravimetric analysis curve of the bio-based epoxy resin containing a Schiff base structure prepared in Example 8. DETAILED DESCRIPTION

[0045] The present invention provides a bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

[0046]

[0047] The bio-based epoxy monomer containing a Schiff base structure provided by the present invention contains a Schiff base structure, and based on the high bond energy and dynamic characteristics of the Schiff base, the thermal stability, flame retardancy and mechanical properties of the bio-based epoxy resin containing a Schiff base structure prepared with the monomer as a raw material are synergistically improved. Moreover, the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has a small molecular weight, a high epoxy value, few side chain substituent groups, a simple structure, high symmetry, and a simple curing process with a curing agent. The obtained bio-based epoxy resin containing a Schiff base structure has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties, and has great application potential in the fields of flame retardancy, self-repair and biodegradable recycling. The present invention also provides a method for preparing a bio-based epoxy monomer containing a Schiff base structure according to the above technical solution, comprising the following steps: mixing a bio-based bisphenol monomer (denoted as VHMBA), epichlorohydrin and a phase transfer catalyst, performing a ring-opening reaction, and then adding an alkali metal hydroxide to perform a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure (denoted as VHMBA-EP);

[0048] The structural formula of the bio-based bisphenol monomer is as follows:

[0049] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0050] In the present invention, the molar ratio of the bio-based bisphenol monomer to epichlorohydrin is preferably 1:2.5-10, and in specific embodiments can be 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0051] In the present invention, the phase transfer catalyst preferably includes one or more of an organic ammonium halide, an organic ammonium bisulfate, pyridine, and an organic amine; the organic ammonium halide preferably includes one or more of tetrabutylammonium bromide, tetrabutylammonium chloride, benzyltriethylammonium chloride, trioctylmethylammonium chloride, dodecyltrimethylammonium chloride, and tetradecyltrimethylammonium chloride; the organic ammonium bisulfate preferably includes tetrabutylammonium bisulfate; and the organic amine preferably includes tributylamine. In the present invention, the molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is preferably 1:0.0125 to 0.2, and in specific embodiments, it can be 1:0.0125, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.1, 1:0.15, or 1:0.2.

[0052] In the present invention, the mixing of the bio-based bisphenol monomer (denoted as VHMBA), epichlorohydrin, and a phase transfer catalyst preferably includes: dissolving the bio-based bisphenol monomer in epichlorohydrin, stirring and mixing, and then adding the phase transfer catalyst and mixing. In the present invention, the stirring and mixing temperature is 20 to 60°C, and in specific embodiments, it can be 20°C, 25°C, 30°C, 40°C, 50°C, or 60°C; the stirring and mixing time is preferably 10 to 40 minutes, and in specific embodiments, it can be 10 minutes, 20 minutes, 30 minutes, or 40 minutes.

[0053] In the present invention, the temperature of the ring-opening reaction is preferably 40-100°C, and in specific embodiments it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; the time of the ring-opening reaction is preferably 1-6h, and in specific embodiments it can be 1h, 2h, 3h, 4h, 5h or 6h.

[0054] In the present invention, the molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is preferably 1:0.5-2, and in specific embodiments, it can be 1:0.5, 1:1, 1:1.5, or 1:2. In the present invention, the alkali metal hydroxide preferably includes at least one of sodium hydroxide and potassium hydroxide. In the present invention, the alkali metal hydroxide is preferably used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is preferably 30-50%, and in specific embodiments, it can be 30%, 35%, 40%, 45%, or 50%.

[0055] In the present invention, the temperature of the ring-closure reaction is preferably ≤0°C, preferably -5 to 0°C, and in specific embodiments, it can be -5°C, -4°C, -3°C, -2°C, -1°C or 0°C; the time of the ring-closure reaction is preferably 2 to 8h, and in specific embodiments, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0056] In the present invention, the mechanism of the ring-opening reaction and the ring-closing reaction is as follows:

[0057]

[0058] After completing the ring-closure reaction, the present invention preferably further comprises: subjecting the obtained ring-closure reaction liquid to organic solvent extraction, washing the obtained organic phase with water until neutral, and removing the solvent to obtain the bio-based epoxy monomer containing a Schiff base structure. In the present invention, the organic solvent preferably includes one or more of methanol, ethanol, dichloromethane, N,N-dimethylformamide and N-methylpyrrolidone. In the present invention, the water washing preferably includes deionized water washing. The present invention does not specifically limit the method for removing the solvent. The method for removing the solvent well known to those skilled in the art can be used to remove water and organic solvent.

[0059] In the present invention, the method for preparing the bio-based bisphenol monomer preferably includes the following steps: neutralizing vanillin amine hydrochloride, and then subjecting it to an amine-aldehyde condensation reaction with vanillin to obtain the bio-based bisphenol monomer. Specifically, vanillin amine hydrochloride is mixed with an alcohol solvent, and an alkaline agent is added for neutralization to obtain a neutralized reaction solution; and the neutralized reaction solution is subjected to an amine-aldehyde condensation reaction with a vanillin solution to obtain the bio-based bisphenol monomer. The preparation route is as follows:

[0060]

[0061] The invention mixes vanillin amine hydrochloride with an alcohol solvent, adds an alkaline reagent for neutralization, and obtains a neutralization reaction liquid.

[0062] In the present invention, the alcohol solvent preferably includes one or more of methanol, ethanol, isopropanol and ethylene glycol; the molar ratio of the vanillin amine hydrochloride to the alcohol solvent is preferably 1:6.5-40, and in specific embodiments it can be 1:6.5, 1:10, 1:15, 1:20, 1:23, 1:25, 1:30, 1:35 or 1:40.

[0063] In the present invention, the alkaline agent preferably includes at least one of an alkali metal carbonate and an alkali metal hydroxide; the alkali metal hydroxide preferably includes at least one of sodium hydroxide and potassium hydroxide; the alkali metal carbonate preferably includes at least one of potassium carbonate and sodium carbonate; the molar ratio of the vanillin amine hydrochloride to the alkaline agent is preferably: 0.3 to 3, and in specific embodiments it can be 1:0.3, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3.

[0064] In the present invention, the mixing time is preferably 5 to 10 minutes, and in specific embodiments can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes; the mixing temperature is preferably room temperature.

[0065] In the present invention, the neutralization temperature is preferably 30-80°C, and in specific embodiments it can be 30°C, 40°C, 50°C, 60°C, 70°C or 80°C; the neutralization time is preferably 10-60 min, and in specific embodiments it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min.

[0066] After obtaining the neutralization reaction liquid, the present invention conducts an amine-aldehyde condensation reaction between the neutralization reaction liquid and a vanillin solution to obtain a bio-based bisphenol monomer.

[0067] In the present invention, the molar ratio of vanillinamine hydrochloride to vanillin is preferably 1:0.65-4, and in specific embodiments can be 1:0.65, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4.

[0068] In the present invention, the solvent in the vanillin solution preferably includes an alcohol solvent, and the alcohol solvent preferably includes one or more of methanol, ethanol, isopropanol and ethylene glycol; the molar ratio of vanillin to solvent in the vanillin solution is preferably 1:3 to 20, and in specific embodiments it can be 1:3, 1:5, 1:10, 1:15 or 1:20.

[0069] In the present invention, the temperature of the amine-aldehyde condensation reaction is preferably 30-80°C, and in specific embodiments it can be 30°C, 40°C, 50°C, 60°C, 70°C or 80°C; the time of the amine-aldehyde condensation reaction is preferably 1-8h, and in specific embodiments it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h or 8h.

[0070] After the amine-aldehyde condensation reaction is completed, the present invention preferably further comprises: pouring the reaction solution obtained from the amine-aldehyde condensation reaction into petroleum ether for precipitation, filtering, and drying the resulting solid component to obtain a bio-based bisphenol monomer. In the present invention, the drying temperature is preferably 30 to 100°C, and in specific embodiments, it can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; the drying time is preferably 4 to 24 hours, and in specific embodiments, it can be 4 hours, 10 hours, 15 hours, 20 hours, or 24 hours.

[0071] The present invention uses bio-based raw material vanillin as the starting material for preparing bio-based bisphenol monomers, thereby avoiding the harm to the environment and human health caused by the release of bisphenol A (BPA) in traditional epoxy resins from the source.

[0072] The present invention also provides the use of the bio-based epoxy monomer containing a Schiff base structure described in the above technical solution in the preparation of epoxy resin.

[0073] The present invention also provides a bio-based epoxy resin containing a Schiff base structure, and the raw materials for preparing the resin include the bio-based epoxy monomer and curing agent described in the above technical solution.

[0074] In the present invention, the curing agent preferably includes one or more of an organic amine curing agent, a carboxylic acid curing agent, and an acid anhydride curing agent; the organic amine curing agent preferably includes one or more of pentamethylenediamine, isophoronediamine, m-xylylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and 4,4'-dithiodiphenylamine; the carboxylic acid curing agent preferably includes one or more of adipic acid, suberic acid, and sebacic acid. In the present invention, the acid anhydride curing agent preferably includes one or more of succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, and trimellitic anhydride. In the present invention, the mass of the curing agent preferably accounts for 10% to 40% of the mass of the bio-based epoxy monomer, and in specific embodiments it can be 10%, 12.8%, 15%, 20%, 24.8%, 25%, 30%, 31.2%, 35%, 36.6%, 38% or 40%.

[0075] In the present invention, the raw materials for preparing the bio-based epoxy resin containing a Schiff base structure preferably also include an accelerator, which preferably includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate, and 2-methyl-4-ethylimidazole. In the present invention, the mass of the accelerator preferably accounts for 0.01% to 10% of the mass of the bio-based epoxy monomer, and in specific embodiments, it can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 3.4%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0076] In the present invention, the glass transition temperature of the bio-based epoxy resin containing a Schiff base structure is preferably ≥95°C, more preferably 95-152°C, and in specific embodiments, it can be 95°C, 122°C, 125°C, 148°C or 152°C; the storage modulus of the bio-based epoxy resin containing a Schiff base structure at 30°C is preferably ≥2700MPa, more preferably 2700-4823MPa, and in specific embodiments, it can be 2700MPa, 3758MPa, 4490MPa, 4654MPa or 4823MPa; the 5% thermal weight loss temperature (N 2 atmosphere) is preferably ≥260°C, and in specific embodiments can be 260°C, 270°C, 273°C, 284°C or 295°C; the residual carbon rate of the bio-based epoxy resin containing a Schiff base structure at 800°C (N2 atmosphere) is preferably ≥20%, more preferably 20-36%, and in specific embodiments can be 20%, 26%, 30%, 35% or 36%; the static tensile strength of the bio-based epoxy resin containing a Schiff base structure at room temperature is preferably ≥55MPa, more preferably 55-71MPa, and in specific embodiments can be 55MPa, 65MPa, 67MPa, 70MPa or 71MPa.

[0077] The Schiff base structure in the bio-based epoxy monomer containing a Schiff base structure provided by the present invention has dynamic chemical properties, and is cured by a carboxylic acid curing agent and an acid anhydride curing agent to form a cross-linked network structure containing dynamic imine bonds and dynamic ester bonds, which synergistically improves the dynamic performance of the epoxy resin cross-linked network. The strategy of applying dynamic chemistry to epoxy resins in the present invention can expand the multifunctionality of epoxy resins while designing high-performance epoxy resins on the molecular structure, thereby solving the problem that thermosetting epoxy resins are "insoluble and infusible" and difficult to recycle after cross-linking and curing. The present invention introduces reversible dynamic covalent bonds into the network of the bio-based epoxy resin containing a Schiff base structure, and then induces the network structure of the thermosetting resin to crack or rearrange through changes in the external environment, so that it has certain degradability and recyclability, which is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0078] The present invention also provides a method for preparing the bio-based epoxy resin containing a Schiff base structure described in the above technical solution, comprising the following steps: mixing a bio-based epoxy monomer and a curing agent, and curing to obtain the bio-based epoxy resin containing a Schiff base structure.

[0079] In the present invention, the mixing temperature is preferably 25-120°C, and in specific embodiments can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C. The present invention has no special limitation on the mixing time, as long as the raw materials can be mixed evenly.

[0080] In the present invention, when the raw materials for preparing the bio-based epoxy resin containing a Schiff base structure also include an accelerator, the mixing is preferably mixing the bio-based epoxy monomer, the curing agent and the accelerator, more preferably mixing the bio-based epoxy monomer and the accelerator, and mixing the resulting mixture with the curing agent.

[0081] After the mixing is completed, the present invention preferably further comprises vacuum degassing the mixed liquid obtained by the mixing, and then performing subsequent curing. In the present invention, the temperature of the vacuum degassing is preferably 25 to 120°C, and in specific embodiments it can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C. The temperature of the vacuum degassing is preferably the same as the temperature of the mixing; the time of the vacuum degassing is preferably 30 to 60 minutes, and in specific embodiments it can be 30 minutes, 40 minutes, 50 minutes or 60 minutes; the vacuum degassing is preferably carried out in an oven.

[0082] In the present invention, the curing preferably includes sequentially performing a first curing and a second curing, and the temperature of the second curing is preferably higher than the temperature of the first curing. In the present invention, the temperature of the first curing is preferably 40 to 120°C, and in specific embodiments, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the time of the first curing is preferably 1 to 10 hours, and in specific embodiments, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours. In the present invention, the temperature of the second curing is preferably 80-200°C, and in specific embodiments, it can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C; the time of the second curing is preferably 1-10 hours, and in specific embodiments, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours. In the present invention, the curing is preferably carried out in a mold, and the mold is preferably preheated before use. The preheating temperature is preferably 40-120°C, and in specific embodiments, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C; the preheating temperature is preferably the same as the temperature of the first curing.

[0083] The preparation method of the bio-based epoxy resin containing a Schiff base structure provided by the present invention has simple process, simple operation, low production cost, is green and environmentally friendly, and is suitable for industrial production.

[0084] The present invention also provides the use of the bio-based epoxy resin containing a Schiff base structure described in the above technical solution or the bio-based epoxy resin containing a Schiff base structure obtained by the preparation method described in the above technical solution in flame retardant materials, self-healing materials or degradable and recyclable materials. The bio-based epoxy resin containing a Schiff base structure provided by the present invention has a high glass transition temperature, excellent mechanical properties and thermal stability, and a dynamic cross-linked network exhibits good dynamic properties. It has great application potential in the fields of flame retardancy, self-healing, and degradable recycling, and is of great significance for the development of recyclable bio-based epoxy resins to replace traditional thermosetting resins.

[0085] The bio-based epoxy monomer containing a Schiff base structure, its preparation method and application, and the bio-based epoxy resin containing a Schiff base structure, its preparation method and application provided by the present invention are described in detail below with reference to the embodiments. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0086] Example 1

[0087] (1) Preparation of bio-based bisphenol monomer (VHMBA): Vanillin amine hydrochloride (0.1 mol) was dissolved in methanol (2.3 mol) and mixed for 10 min. Anhydrous potassium carbonate (0.1 mol) was then added and the temperature was raised to 55°C and stirred for 30 min to obtain a neutralization reaction solution. Vanillin (0.1 mol) was dissolved in methanol (1.2 mol), and the obtained vanillin solution was added to the neutralization reaction solution. The reaction was carried out at 55°C for 4 h. After the reaction, the reaction solution was poured into petroleum ether for precipitation, filtered, and the obtained solid component was placed in a vacuum oven at 80°C and dried for 12 h to obtain VHMBA (24.8 g, yield 87%).

[0088] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 40 ° C for 30 min, and tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added. The temperature was raised to 80 ° C for reaction for 2 h, and then cooled to room temperature and treated in an ice bath. When the temperature dropped below 0 ° C, a 40% mass fraction of sodium hydroxide aqueous solution (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h. The organic phase was extracted with ethyl acetate and washed with deionized water until neutral. The ethyl acetate was completely removed by rotary evaporation to obtain VHMBA-EP (32.3 g, yield 81%).

[0089] Example 2

[0090] (1) Preparation of bio-based bisphenol monomer (VHMBA): Vanillin amine hydrochloride (0.1 mol) was dissolved in methanol (2.3 mol) and mixed for 10 min, then anhydrous potassium carbonate (0.1 mol) was added. The temperature was raised to 60°C and stirred for 30 min to obtain a neutralization reaction solution; vanillin (0.1 mol) was then dissolved in methanol (1.2 mol), and the obtained vanillin solution was added to the neutralization reaction solution and reacted at 60°C for 6 h. After the reaction, the reaction solution was poured into petroleum ether for precipitation, filtered, and the obtained solid component was placed in a vacuum oven at 80°C and dried for 12 h to obtain VHMBA (25.8 g, yield 90%).

[0091] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 60 ° C for 30 min, and tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added. The temperature was raised to 80 ° C for reaction for 4 h, cooled to room temperature and then treated in an ice bath. When the temperature dropped below 0 ° C, a 40% mass fraction of sodium hydroxide aqueous solution (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h. The organic phase was extracted with ethyl acetate and washed with deionized water until neutral. The ethyl acetate was removed by rotary evaporation to obtain VHMBA-EP (31.5 g, yield 79%).

[0092] Example 3

[0093] (1) Preparation of bio-based bisphenol monomer (VHMBA): Vanillin amine hydrochloride (0.1 mol) was dissolved in methanol (2.3 mol) and mixed for 10 min, then anhydrous potassium carbonate (0.1 mol) was added. The temperature was raised to 60°C and stirred for 30 min to obtain a neutralization reaction solution; vanillin (0.1 mol) was then dissolved in methanol (1.2 mol), and the obtained vanillin solution was added to the neutralization reaction solution and reacted at 60°C for 6 h. After the reaction, the reaction solution was poured into petroleum ether for precipitation, filtered, and the obtained solid component was placed in a vacuum oven at 80°C and dried for 12 h to obtain VHMBA (25.8 g, yield 90%).

[0094] (2) Preparation of bio-based epoxy monomer containing Schiff base structure (VHMBA-EP): VHMBA (0.1 mol) was dissolved in epichlorohydrin (1.0 mol), stirred at 40 ° C for 30 min, and tetrabutylammonium bromide (10.3 mmol) as a phase transfer catalyst was added. The temperature was raised to 80 ° C for reaction for 2 h, and then cooled to room temperature and treated in an ice bath. When the temperature dropped below 0 ° C, a 40% mass fraction of sodium hydroxide aqueous solution (0.2 mol) was added, and the system was kept at this temperature for reaction for 5 h. The organic phase was extracted with ethyl acetate and washed with deionized water until neutral. The ethyl acetate was completely removed by rotary evaporation to obtain VHMBA-EP (32.3 g, yield 81%).

[0095] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the bio-based epoxy monomer prepared in Example 3. It can be seen that the present invention successfully prepared a bio-based epoxy monomer having the structure shown in Formula I.

[0096] Epoxy value test: The theoretical epoxy value of the VHMBA-EP prepared in Example 1 was 0.501 mol / 100 g, and the actual tested epoxy value was 0.470 mol / 100 g; the theoretical epoxy value of the VHMBA-EP prepared in Example 2 was 0.501 mol / 100 g, and the actual tested epoxy value was 0.480 mol / 100 g; the theoretical epoxy value of the VHMBA-EP prepared in Example 3 was 0.501 mol / 100 g, and the actual tested epoxy value was 0.460 mol / 100 g.

[0097] Example 4

[0098] Preparation of a bio-based epoxy resin containing a Schiff base structure: 1.56 g of the curing agent 4,4'-dithiodiphenylamine and 5 g of VHMBA-EP prepared in Example 1 were mixed uniformly at 80°C, and air bubbles were removed in a vacuum at 80°C for 30 minutes. The mixture was poured into a mold that had been preheated in a 100°C forced air oven, and the mixture was first cured at 100°C for 4 hours and then at 150°C for 4 hours. The mixture was cooled to room temperature and then demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0099] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 148℃, and the storage modulus at 30℃ is 3758MPa (see Figure 2 ); 5% thermal weight loss temperature under N2 atmosphere reaches 260 ℃, and the residual carbon rate at 800 ℃ is 36% (see Figure 3 ); the static tensile strength at room temperature is 70MPa.

[0100] Example 5

[0101] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.64 g of the curing agent 1,5-pentanediamine and 5 g of VHMBA-EP prepared in Example 1 were mixed uniformly at 25°C, and bubbles were removed under vacuum at 25°C for 20 minutes. The mixture was poured into a mold that had been preheated in a 60°C forced air oven, and the mixture was first cured at 60°C for 6 hours and then at 120°C for 10 hours. The mixture was cooled to room temperature and then demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0102] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 125℃, the storage modulus at 30℃ is 4823MPa, and the elasticity (see Figure 4 ); 5% thermal weight loss temperature under N2 atmosphere reaches 270℃, and the residual carbon rate at 800℃ is 26% (see Figure 5 ); the static tensile strength at room temperature is 65MPa.

[0103] Example 6

[0104] Preparation of a bio-based epoxy resin containing a Schiff base structure: 1.24 g of the curing agent 4,4'-diaminodiphenylmethane and 5 g of VHMBA-EP prepared in Example 1 were mixed uniformly at 90°C, followed by vacuum removal of bubbles at 90°C for 30 minutes. The mixture was then poured into a mold that had been preheated in a 100°C forced air oven, first cured at 120°C for 4 hours, then second cured at 150°C for 2 hours, and then cooled to room temperature and demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0105] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 152℃, and the storage modulus at 30℃ is 2700MPa (see Figure 6 ). The 5% thermal weight loss temperature under N2 atmosphere reaches 295℃, and the residual carbon rate at 800℃ is 20% (see Figure 7 ); the static tensile strength at room temperature is 67MPa.

[0106] Example 7

[0107] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.3 g of zinc acetylacetonate and 5 g of VHMBA-EP prepared in Example 2 were mixed uniformly at 100° C., and then 1.25 g of a curing agent, succinic anhydride, was added. After the prepolymer was completely mixed, air bubbles were removed in a vacuum at 90° C. for 30 minutes, and then the mixture was poured into a mold that had been preheated in a 120° C. forced air oven. The mixture was first cured at 120° C. for 4 hours, and then secondly cured at 150° C. for 6 hours. After cooling to room temperature, the mixture was demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0108] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 122℃, and the storage modulus at 30℃ is 4654MPa (see Figure 8 ); 5% thermal weight loss temperature under N2 atmosphere reaches 284 ℃, and the residual carbon rate at 800 ℃ is 35% (see Figure 9 ); the static tensile strength at room temperature is 71MPa.

[0109] Example 8

[0110] Preparation of a bio-based epoxy resin containing a Schiff base structure: 0.17 g of 1,5,7-triazabicyclo[4.4.0]decene-5-ene and 5 g of VHMBA-EP prepared in Example 2 were mixed uniformly at 80° C., and then 1.83 g of adipic acid as a curing agent was added. After the prepolymer was completely mixed, bubbles were removed by vacuum at 80° C. for 30 minutes and then poured into a mold that had been preheated in a 120° C. forced air oven. The mixture was first cured at 120° C. for 4 hours and then secondly cured at 160° C. for 6 hours. After cooling to room temperature, the mixture was demolded to obtain a bio-based epoxy resin containing a Schiff base structure.

[0111] The glass transition temperature of the bio-based epoxy resin containing Schiff base structure is 95℃ and the storage modulus at 30℃ is 4490MPa (see Figure 10 ). The 5% thermal weight loss temperature under N2 atmosphere reaches 273℃, and the residual carbon rate at 800℃ is 30% (see Figure 11 ); the static tensile strength at room temperature is 55MPa.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A bio-based epoxy monomer containing a Schiff base structure, having a structure shown in Formula I:

2. The method for preparing the bio-based epoxy monomer containing a Schiff base structure according to claim 1, comprising the following steps: The bio-based bisphenol monomer, epichlorohydrin and a phase transfer catalyst are mixed to carry out a ring-opening reaction, and then an alkali metal hydroxide is added to carry out a ring-closing reaction to obtain the bio-based epoxy monomer containing a Schiff base structure; The structural formula of the bio-based bisphenol monomer is as follows:

3. The preparation method according to claim 2, characterized in that The molar ratio of the bio-based bisphenol monomer to epichlorohydrin is 1:2.5-10; The phase transfer catalyst includes one or more of organic ammonium halides, organic ammonium bisulfate, pyridine and organic amines; The molar ratio of the bio-based bisphenol monomer to the phase transfer catalyst is 1:0.0125-0.2; The ring-opening reaction temperature is 40-100°C and the time is 1-6 hours; The molar ratio of the bio-based bisphenol monomer to the alkali metal hydroxide is 1:0.5-2; The alkali metal hydroxide is used in the form of an alkali metal hydroxide aqueous solution, and the mass concentration of the alkali metal hydroxide aqueous solution is 30-50%; The temperature of the ring-closing reaction is less than 0° C., and the time is 2 to 8 hours.

4. Use of the bio-based epoxy monomer containing a Schiff base structure according to claim 1 in the preparation of epoxy resin.

5. A bio-based epoxy resin containing a Schiff base structure, wherein the raw materials for preparing the resin include the bio-based epoxy monomer according to claim 1 and a curing agent.

6. The bio-based epoxy resin containing a Schiff base structure according to claim 5, characterized in that: The curing agent includes one or more of an organic amine curing agent, a carboxylic acid curing agent and an acid anhydride curing agent; The mass of the curing agent accounts for 10 to 40% of the mass of the bio-based epoxy monomer.

7. The bio-based epoxy resin containing a Schiff base structure according to claim 5, characterized in that: The preparation raw materials also include a promoter, which includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, imidazole, zinc acetylacetonate and 2-methyl-4-ethylimidazole; The mass of the accelerator accounts for 0.01 to 10% of the mass of the bio-based epoxy monomer.

8. The method for preparing the bio-based epoxy resin containing a Schiff base structure according to any one of claims 5 to 7, comprising the following steps: The bio-based epoxy monomer and the curing agent are mixed and cured to obtain the bio-based epoxy resin containing the Schiff base structure.

9. The preparation method according to claim 8, characterized in that The curing includes sequentially performing a first curing and a second curing; the first curing temperature is 40 to 120° C. and the time is 1 to 10 hours; the second curing temperature is 80 to 200° C. and the time is 1 to 10 hours; the second curing temperature is higher than the first curing temperature; When the raw materials further include an accelerator, the mixing is to mix the bio-based epoxy monomer, the curing agent and the accelerator.

10. Use of the bio-based epoxy resin containing a Schiff base structure according to any one of claims 5 to 7 or the bio-based epoxy resin containing a Schiff base structure obtained by the preparation method according to any one of claims 8 to 9 in flame retardant materials or self-healing materials.

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